A common method for the manufacture of asphalt shingles is the production of a continuous strip of asphaltic shingle material followed by a shingle cutting operation which cuts the strip into individual shingles. In the production of asphaltic strip material, either an organic felt mat or a glass fiber mat is passed through a coater containing hot liquid asphalt to form a tacky coated asphaltic strip. Subsequently, the hot asphaltic strip is passed beneath one or more granule applicators which apply protective surface granules to portions of the asphaltic strip material. Typically, the granules are dispensed from a hopper at a rate which can be controlled by making manual adjustments on the hopper.
Not all of the granules applied to the hot, tacky, coated asphaltic strip adhere to the strip. Typically, the strip material is turned around a slate drum to press the granules into the tacky asphalt and to invert the strip. The non-adhered granules then drop off the strip. These non-adhered granules, which are known as backfall granules, are usually collected in a backfall hopper for recycling.
In the manufacture of colored shingles, two types of granules may be employed. Headlap granules are granules of relatively low cost used for portions of the shingle which are to be covered up. Colored granules or prime granules are of relatively higher cost and are applied to the portion of the shingle which will be exposed on the roof.
To provide a color pattern of pleasing appearance, the colored portion of the shingles may be variegated or provided with areas in different colors. Usually the shingles have areas of background color granules separated by highlighted areas of granule deposits of different colors or different shades of the background color. The highlighted areas, referred to as blend drops, are typically made from a series of granule containers applied by means of feed rolls. The length and spacing of each area on the sheet is dependent on the speed of the feed roll, the relative speed of the sheet and the length of time during which the drop is made. A programmable controller controls the speed of the sheet and the times of the blend drops.
A common method for manufacturing a variegated shingle involves applying granules of a first color or blend drops to spaced first areas on the moving hot, tacky asphaltic strip. Granules of a second or background color are then applied to the areas between the first area blend drops. However, imperfections in feeding the first granules creates irregular leading and trailing edges for the first area blend drops. At high production speeds, the effects of the granule feeding imperfections are accentuated. Typically, the granules will be deposited sooner in the center region of the moving strip than at the outer sides of the leading edge of each first area. The granule deposition also will tend to terminate later in the center region of the moving strip than at the outer sides. This can result in an oval shape for each first area which becomes more accentuated as production speeds increase. Further, granule feeding imperfections can cause the density of the granules at the leading and trailing edges of each first area to be lower than in the center of the area. Difficulties in feeding the first color granules have prevented using this method for manufacturing high-quality variegated shingles at high production speeds.
One well-known prior-art technique for manufacturing variegated shingles involved the application of the background color granules over the entire exposed tacky surfaces of the shingles. Adhesive such as hot asphalt is applied to the background color granules on the sheet in the areas where the blend drops are to be applied--and then the blend drops are applied and stick only to the tacky areas. The double layers of granules in the blend drop areas make these shingles relatively expensive, heavy and inflexible.
One of the problems with typical granule application equipment is that the feeder rolls depend on mechanical movement (rotation) to index to the next position to enable another blend drop to fall onto the moving coated asphalt sheet. Usually the granules are discharged from a hopper onto a fluted roll from which, upon rotation, the granules are discharged onto the coated asphaltic sheet. The roll is ordinarily driven by a drive motor, and the roll is positioned in the drive or non-drive position by means of a brake-clutch mechanism. The requirement for mechanical action has inherent limitations which prevent a very precise beginning and ending to the blend drop. Also, once the mechanical action takes place, there is a short time lag as gravity takes effect on the granules. Consequently, there is a limit to the sharpness of the blend drops on the shingle. As shingle manufacturing lines go up in speed, the lack of sharpness is accentuated and the distinction between the blend drop and the background color becomes fuzzy. The lack of sharpness puts a severe limitation on the kinds of designs and color contrasts which can be applied to shingles at high production speeds.
Another cause of the impreciseness of typical granule-depositing techniques is that the feeders typically depend on gravity exclusively, not only for directing the granules from the hopper to the moving coated asphalt sheet, but also for movement of the granules within the hopper itself. The use of gravity to move the granules within the hopper or discharge apparatus itself has granule feed rate limitations. There has been no easy way to control the rate of flow of the granules for the entire blend drop.
A recently developed improved method for depositing granules onto the moving coated asphalt sheet uses a pneumatic control to provide a relatively high degree of preciseness in depositing the granules. The newly developed method provides relatively instantaneous control of the flow of granules. The flow of granules is started, stopped and controlled by providing pneumatic pressure changes in a buffer chamber positioned adjacent an accumulation of granules in a granule nozzle. It has been found, however, that although the pneumatically controlled granule blend drop apparatus provides a very sharp leading edge for a blend drop, it produces a fuzzy or less sharp trailing edge for the blend drop. An improved process would provide for manufacturing variegated shingles at high speeds in which the blend drops have both a sharp leading edge and a sharp trailing edge.